The continued evolution of application programs, such as word processing and desktop publishing programs, has provided users with a great deal of versatility and control in the appearance of documents created with these types of programs. A significant factor in this area is the ability to influence the layout of textual and symbolic characters on a page. Initially, the character fonts that were available for use in these types of programs were relatively static, in the sense that their shapes and positioning were rigidly fixed according to a predefined set of rules. As new fonts have been developed, the technology pertaining to the appearance and layout of characters has also evolved, so that new capabilities are continuously being added to fonts. As a result, it is now possible to control a number of different parameters which determine the appearance and layout of characters in a line of text. Examples of these parameters include the identification of the specific glyphs that define the appearances of the characters, substitution of contextual letterforms and ligatures, the positioning of the glyphs relative to one another, hanging punctuation, and optical alignment of a line of characters.
To provide these types of capabilities, a given font is comprised of more than just the glyphs which determine the appearances of the individual characters. In particular, the font definition consists of a number of data tables that relate to various parameters which control the implementation of the font. For instance, a TrueType font comprises a file that may contain up to thirty or more tables that determine the layout and other characteristics of the font. Examples of the types of data in these tables include kerning, i.e. spacing between characters, the metrics or dimensions of glyphs, variable properties such as line widths, and the like. The information provided by these tables is employed for a number of different purposes. For instance, some processes may rely upon a table of the names of various font styles, to display in a menu or dialog box. Another use of the tables occurs when a line of characters is to be Laid out for display or printing purposes. One example of a technology which lays out a line of text pursuant to the data in such tables is described in U.S. Pat. No. 5,416,898, the disclosure of which is incorporated herein by reference.
As font technology continues to evolve over time, new capabilities are constantly being added, to enhance the versatility and control over the appearance of characters. The added capabilities are generally accompanied by new data tables. An unfortunate consequence of this development is the fact that older fonts may not contain all of the tables necessary to conform to the latest capabilities. As an example, if an attempt is made to employ an older font which does not contain the latest tables, during the operation of a line layout processor that makes use of the newer tables, the results can range from an unaesthetic appearance to linguistically incorrect text.
In an effort to overcome the limitations associated with the use of older fonts, various tools have been made available to permit font developers to add new tables to existing fonts. However, there may be a reluctance by developers to alter the contents of a font once it has been accepted. Furthermore, even if a font is updated to incorporate the newer data tables, users must become aware of, and acquire, the updated fonts before they can be successfully used with the newer font processing technologies.
Accordingly, it is desirable to provide a mechanism via which data tables that are needed to properly process the glyphs of a font can be automatically synthesized if they are not part of the original font definition. Further in this regard, it is desirable to be able to synthesize and employ such tables in a manner which does not affect the original definition of the font.